|
Using OnChange to Fill a Drop-Down Menu
From time to time it becomes necessary to have a drop-down menu fill
dynamically based on what a user chooses from another drop-down menu. This
can be very useful when using a form to add records to a table in a database
that includes fields linked to another table, in a one to many
relationship. I.E. A program type table called "Programs" may
have another table called "Code" that is linked to it via the "ProgType"
field (the primary key of the "Programs" table). But how do we
set this up?
OnChange:
The best way I've found to do this is via an "onChange" event
using JavaScript. The calling "select" statement will contain the
reference to a function utilizing this event:
onChange="getCode(this)"
Then a JavaScript function (placed between the
tags) called "getCode()" then passes the value selected via the
ProgType menu back to the same page via a window.location method:
window.location = "onchange.asp?ProgType=" +
ProgType
Within the same page you will need to add a querystring that passes the
ProgType value into a "ProgType" variable. This value is then
used to retrieve the Code values and fills the Code drop-down menu.
Note: make sure you test for a value in the CodeType variable and if it
isn't blank or null, use it to retrieve the "selected" menu item that
will appear in the ProgType down menu.
Sample
|
